How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Rixster Your Own Question
Rixster, ASE Certified Technician
Category: Car
Satisfied Customers: 282
Experience:  Owner Rix Automotive & Mobile Repair 27+ Years Exp. with all makes and models cars and Lt. Trucks
Type Your Car Question Here...
Rixster is online now
A new question is answered every 9 seconds

96 olds cutlass supreme: temp gauge..the upper hose cool..coolant

Customer Question

I have a 96 olds cutlass supreme. The temp gauge read hot so I found the upper hose cool and changed the thermostat. While I was at it I decided to change the coolant/fan sensor. the battery was disconnected until I finished. When I started the vehicle I noticed that the upper hose was now hot but the fan never came on and the temp gauge reached the red mark. Thinking I got a defective sensor, I put the old one back in. Now both fans come on (a/c & radiator) when I first start up cold and the gauge never gets hot and a/c doesn't blow cold. What could cause this?
Submitted: 8 years ago.
Category: Car
Expert:  Rixster replied 8 years ago.

Hello! I'm Rixster...

I'd ask you to check some things for me if you would it can benefit our Diagnosis...

Were there any leaks you found?

Have you checked the oil? Do!

Let me know what you find...

Thanx! -Rixster

Expert:  Rixster replied 8 years ago.
Customer: replied 8 years ago.
There were no leaks. I was washing my car with it idling and when I was done, I got in to drive and noticed the temp gauge read hot in the red. The fan was on so I did some checking and noticed that the upper radiator hose was cool. I changed the thermostat to fix the problem and decided to change the coolant/fan sensor next to the thermostat (3 prong) while I was there since it was much easier to change while the throttle body was removed. After starting the vehicle and filling the radiator, I bleed off the air using the 2 bleeders at the thermostat and the pipe assembly. Waiting for the engine to warm up, I noticed that the temp gauge finally went tothe red mark again and when I checked under the hood, I noticed that the fan did not come on. I assumed that the new coolant/fan sensor was defective since the fan had come on with the old sensor so I took out the new one and put the old one back in. Now as soon as I start, both fans come on and the temp gauge reads cool all the time, but the a/c has shut down. It's like it's reading engine overheat but the gauge reads cool. The upper hose now is circulating fine. The oil level is fine also.
Customer: replied 8 years ago.
What should I look for and check next? Also now my check engine light is on. I don't have a scanner but I can guess that the codes will relate to coolant sensor and a/c and overheating. The a/c previously worked fine and I'm sure that the coolant sensor is sending the signal of overheating and cutting it off, even though the gauge reads cool. It will never get to operating temperature with both fans running. It does'nt matter whether or not the a/c is turned on. Both fans run at all times.
Expert:  Rixster replied 8 years ago.

Yes it will get to operating temp. but your fans should not run at all times.

It sounds to me like there is a sensor problem. Did you replace the cooling fan switch or the coolant temp sensor?

The Coolant temp sensor is a two prong sensor with a yellow and a black wire going to it. The PCM gets a signal from the coolant temp sensor which when interpreted ques the cooling fans. There really is no specific Fan Switch.

Also This system is a real pain to purge all the air out of. If you have any bubbles in the system it can send you on some real good wild goose chases. Be sure the system is burped properly. It is possible to aquire a defective Coolant Temp. Sensor. I've had a few in my time. Buy the best quality one you can find if not an OEM part. This assures a good clean reading for the PCM.

If you need further assistance I'm here.

Thanx! -Rixster

Customer: replied 8 years ago.
The coolant sensor that controls the PCM also serves as a fan switch. It has 3 prongs and has a duel function. What bothers me is that it was working normally before. The fan would come on when it got to just over 3/4 hot and was on before changing thermostat. After changing coolant sensor the fan did not come on at all. When I put back the old one, now both fans come on right away and stay on and my a/c has shut down. It's like I have a poltergiest. Should I check the fan relays and try another coolant sensor?
Expert:  Rixster replied 8 years ago.

The Coolant temp sensor for this vehicle only has two prongs and has a two wire connector that has a yellow and a black wire going to it.

I don't know what you think is the Coolant temp sensor but unless this is something new I don't think you changed the right one. I may be wrong but all my diagrams show two wires...




Yes it is possible to have a faulty sensor so If at all possible I'd go ahead and try another one in there to see what's up.

Let me know what you find...

Thanx! -Rixster

Customer: replied 8 years ago.
Your diagram shows a MAP sensor. My vehicle has a MAF sensor and the ECT sensor has 3 prongs located on the intake manifold next to the thermostat. The wire connector has 3 wires. This is a 3.1 V-6 engine not a 4 cyl. So far you have not helped me find the problem or what caused it.
Expert:  Rixster replied 8 years ago.

Well I'm here to argue with you sir. I'm trying to help!

I Know What a 3.1 V6 is! I'm just telling you what I have in front of me.

The Diagram I sent you is for a 1996 Oldmobile Cutlass Supreme with a 3.1 V6.

If your vehicle has a Mass Airflow Sensor then I'm looking at the wrong one. Can you give me the 8th V.I.N. digit and I'll try to find the correct diagram for you.

As for helping you so far... I HAVE answered your question as to what can cause this...

If it worked before and all you did was change t-stat and the Coolant Temp. Sensor

then it didn't work as you'd expect, You have got to have a faulty sensor! If you have 35 Years as a tech then you must know... What else could it be?

If you get me the 8th digit I can get you a diagram.


I found this diagram for a late 96-97 model...



If you look at the coolant temp sensor it still has the yellow and the black wires but has a dark green wire for a cluster feed.

I'm trying to help!

Thanx! -Rixster


Customer: replied 8 years ago.
The eighth digit is "M"
Customer: replied 8 years ago.
I don't have a wiring diagram or scanner. I would like to know how the relays tie into that circuit and if the ECM relay ties into the same circuit.
Expert:  Rixster replied 8 years ago.
I just posted an updated diagram I found. I think this might be it.
Customer: replied 8 years ago.
For some reason, the diagram still shows a MAP sensor. It would be helpful to have the diagram showing the cooling fan relay cicuit and the ECM relay. This is a "w" body vehicle (4th digit). 96 cutlass supreme SL.
Expert:  Rixster replied 8 years ago.



I'm having a bit of a time finding an ECM Relay Diagram but I will keep looking. Meantime here is this one...

I hope it helps!

Customer: replied 8 years ago.
That last diagram is a big help. Let me know if you find one for the ECM relay. I noticed that there is power all the time to the relays. One of them could be shorted or stuck in the run mode. Is there any specifications for the relays? In looking up parts, all the relays have the same part number.
Customer: replied 8 years ago.
I will work on this tomorrow and get back to you.
Expert:  Rixster replied 8 years ago.

That'll be cool!

If I've helped at all feel free to click ACCEPT!

Customer: replied 8 years ago.
I'm sorry but I cannot accept your answer. The question was "what can cause this". You spent most of your time debating that I was giving you the wrong information about what sensor I had. You supplied me with a wiring diagram that was not specific for my vehicle. You need to listen more to what the customer is asking for. you never mentioned that a relay can cause this problem. It should have been obvious that since the old sensor was working fine before and was put back, that there was something else to look for.Your wiring diagram was for a chevrolet since it showed a MAP sensor. The other diagram was a general, not make,model, and year specific. It should have showed the ECM (ign system) relay in the same area of the 2 cooling fan relays. As an expert, you are suppossed to guide the customer to the solution of the problem,not the other way around.
Expert:  Rixster replied 8 years ago.

You can say what you will. My diagrams came from alldata. They were from the page pulled up under this year make and model you gave me.

If you are 35 year ASE Certified you should know how these data bases are generalized sometimes.

I apologize for not having a library of OEM service manuals at your disposal!

Good Luck!